A quick Google search led to this explanation but this was not the exact issue for me. In my case there was a reference to a user control .ascx file in the page layout that had not been deployed to the bin folder of the web application. Once this resource was deployed to the path the page layout expected to see it in the page loaded without a problem.

Update - another reason for this error is if your page layout has become customized. This will happen if you edit the page layout using SharePoint Designer.

I recently wrote a post that included a .wsp file. In the comments a reader asked for more information on how to deploy this to their SharePoint environment.

I suppose it is a sign that I have been developing SharePoint solutions for too long when I start to assume that this is basic knowledge that everybody has! To try and make amends for this assumption here is a quick guide to deploying a wsp using stsadm and central admin. The first part is generic to all .wsp solutions and the second part is specific to the deployment of a web part that has been added using a SharePoint solution.

First we need to use STSADM.exe to add the .wsp file to the SharePoint farm.

Open a command window and drag stsadm.exe onto it and use the following command to add the solution to the solution store.

stsadm -o addsolution -filename c:\solution.wsp

You can also use stsadm to deploy the solution but here I am going to describe the point and click method using SharePoint Central Admin which does the same thing.

Open SharePoint Central Admin and select the Operations tab.

Select Solution Management.

Click the link to the .wsp solution you just added.

Click Deploy Solution - If the solution is not globally deployed select the web applications you want to deploy to.

Click OK.

The solution is now deployed to the web applications you selected or to all web applications if it deployed globally. This is not the end of the deployment process though. If the solution contains a web part there are still a few steps to go before it will be displayed on your site. To add the web part to a page on your site do the following:

Navigate to the site collection where you want to place the web part and go to Site Settings and Site Collection Features (this assumes that the feature is scoped at the site collection level, sorry for making more assumptions that you understand scopes but that is another post and something that other people have already written plenty about if you want to find out more).

Activate the feature that contains the web part that has been deployed in the solution.

Next, go to Site Settings and Web Parts and click New.

Select the web part to add it to the wbe aprt gallery for that site collection.

The web part is now ready to be added to a page in the usual way - edit page, add web part to zone, browse to web part.

When I mentioned that I was developing a Twitter web part to Mirjam van Olst she asked if it would be possible to work on it with me. So thanks to Mirjam, in the true spirit of international collaboration, we are now able to bring you an updated version of the web part which is more secure and easier to deploy.

Improvements include -

The password input now uses a password textbox to protect the Twitter credentials

I thought I would have a go at creating a web part to display a Twitter public timeline within SharePoint. The reason for creating this web part is so that it can be used by project teams that are spread over several offices/countries to stay in touch and feel more connected without having to invest a lot of time emailing each other or talking on the phone. Twitter is ideal for this kind of light weight communication as it restricts the user to sending short, to the point messages.

Before starting I had a quick look on the web to see if I was reinventing the wheel. Michael Gannotti suggests this solution using javascript and the CEWP but I wanted something that we would have a little more control over in terms of html markup and branding and that wasn't limited to the CEWP being available. I also wanted to have the possibility of extending the web part to include other functionality in the future such as not just being able to display tweets but to also send them.

The web part is configurable using two custom attributes - username and password. This allows you to display any users public timeline assuming you have the password. To set it up for use with a project team public timeline you should create a Twitter account for the project and then follow the members of the team to see a timeline that displays tweets from each of the members.

At the bottom of this post there are links to the .wsp file which can be deployed to SharePoint using stsadm.exe and a .css file so that you can see how I chose to style the web part but obviously you could brand it any way you want.